Hengyu Wang

Optimal design of wheel profiles for high-speed trains

The high maintenance cost of high-speed wheels due to wear and rolling contact fatigue is a major problem in the commercial operation of high-speed trains in China. In order to understand the wear behavior of high-speed wheels and its influence on the motion stability of high-speed trains, the worn profiles and the work-hardening of the wheels of the CRH3 high-speed trains that operate on the Wuhan–Guangzhou line were monitored in different periods during service; in particular, the influence of hollow wear of the wheel on the lateral acceleration of the bearing-box was investigated in detail. A new wheel profile design method was suggested to reduce the hollow wear by seeking an optimization match of the wheel profiles, the vehicle’s suspension systems, and the wear behavior of wheels in service. The feasibility of the method was verified by numerical simulation using the operation conditions of CRH3 high-speed trains on the Wuhan–Guangzhou line. A new wheel profile was designed using this method. The wheel/rail contact performance and the vehicle’s dynamic behavior resulting from the designed new wheel were investigated in detail and compared with those of the original wheel. The wear behavior of the designed new wheel profile was predicted based on wear data measured on the original wheel. The results show that compared with the original wheel profile, the designed new wheel profile can improve the wheel/rail contact state, reduce the contact stress level, and lower the friction power of wheel and rail. The extent of hollow wear on the new wheel is significantly decreased and the vehicle has improved dynamic behavior when wheelsets with the designed new profile are used. Thus, the period before re-profiling is required can be effectively extended.

An investigation into the mechanism of metro rail corrugation using experimental and theoretical methods

Severe short-pitch rail corrugation was found to have occurred on four types of track on the same metro line. Field investigations found that, even with the same operation conditions, the corrugations had different wavelengths for the different types of track. Impact hammer tap tests were conducted to investigate the dynamic behaviour of the tracks. The test results showed that, in the investigated metro, short-pitch corrugations are associated with the resonance behaviour of the tracks. The test results also showed that the corrugations on the investigated tracks are not caused by torsional vibration due to the wheelsets. Numerical simulations were conducted to identify the resonance behaviour that is could not be observed in the impact hammer tests due to the limitations in the test method. Three-dimensional finite element models for the four types of track were established and they were used to study the dynamic characteristics of the different tracks. The resonance frequencies and modes that are related to the generation of the corrugation were clearly identified in the numerical modelling studies; this further verifies the relationship between the formation of corrugation and the resonance behaviour of the tracks. The effect of a low value of the fastener stiffness on the dissipation of wheel/rail vibration energy was investigated with the help of numerical simulations. Both experimental and numerical results showed that the resonance behaviour of track structures is of great importance in determining the initiation, characteristics and development of the short-pitch corrugation on the investigated tracks.

Experimental study on the wear and damage behavior of different wheel/rail materials:

The objective of this study is to investigate the effect of hardness and contact stress on wear and damage behavior of wheel and rail materials using a rolling-sliding simulation facility. Furthermore, the hardness matching and damage mechanism of wheel and rail materials are explored and clarified using several techniques. The wear weight of wheel rollers increases nearly linearly with the hardness ratio of rail and wheel rollers. However, the wear weight of rail rollers linearly decreases at the same conditions. An increase in the hardness of the wheel material results in the damage mechanism of the wheel roller changing from small pitting and adhesion wear to delamination wear. Then the rail roller shows severe shelling damage. Practically, the matching of the hardness of wheel and rail materials shows significant potential for alleviating wear and surface damage. An increase in the contact stress results in the wear of wheel and rail rollers becoming more severe. The damage mechanism changes from small shelling to serious delamination damage and oxidation wear. The main compositions of wear debris are the oxide Fe2O3 and martensite. Accordingly, decreasing the contact stress is an effective measure for alleviating wear and damage of heavy-haul wheel and rail materials.

Analysis of wheel/rail adhesion under oil contamination with surface roughness

The objective of this study is to investigate the adhesion characteristics of wheel/rail under oil contamination with consideration of surface roughness using a three-dimensional model of wheel/rail in rolling contact. A partial elastohydrodynamic lubrication theory is employed in the model. An under-relaxation revision on the film thickness is used to keep the simulation procedure stable. The dependence of the wheel/rail adhesion coefficient on train speed, surface roughness amplitude, parameter of roughness orientation and axle load is studied under oil contamination. Moreover, the numerical solutions of a two-dimensional model are compared with those of the three-dimensional model. In addition, a good agreement has been found between the numerical results and the experimental results obtained by a JD-1 wheel/rail simulation facility, which consists of a small wheel roller serving as locomotive or rolling stock wheel and a large wheel roller serving as rail.

Numerical and experimental investigation on adhesion characteristic of wheel/rail under the third body condition

A numerical model of wheel and rail lubricated by a third body was established using the partial elasto-hydrodynamic lubrication theory and multi-grid method. The effects of rolling speed, surface roughness, contact load, wheel diameter, and viscosity of third body on adhesion coefficient are explored. The results show that the rolling speed, surface roughness, and the viscosity of third body have a significant influence on adhesion coefficient when the wheel/rail interface is lubricated under oil and water conditions. Furthermore, to verify the precision of the numerical calculating results, some experiments were carried out by means of a JD-1 wheel/rail simulation facility. The results show that there is same changing trend and almost same adhesion coefficient between the curves of numerical and experimental results. The relative difference between the numerical and experimental results is less than 10%. This numerical method can be used to explore the adhesion coefficient of wheel/rail under the third body condition.

Optimal design of rail grinding patterns based on a rail grinding target profile

Based on the grinding target profile of the rail and the grinding capacity of a single grinding stone, a numerical calculation method for rail grinding patterns that includes grinding angle and grinding power of each grinding stone of the GMC96 rail grinding train was designed and established. By means of this numerical method, the grinding pattern of each grinding pass was optimized and the rail head profile after grinding was calculated. Furthermore, a method for the evaluation of the grinding quality is provided. The results indicate that in multipass rail grinding, a sequence of grinding passes – where the greatest grinding effort is applied on the earlier passes, with the last pass applying reducing levels of grinding effort – produces the highest conformance to the target grinding profile. For example, when rail grinding is planned for two passes, applying 60% of the total grinding effort on the first pass and 40% on the second pass decreases the final grinding error by 7.3%.